Survival Efficacy of Combined Radiotherapy and Immunotherapy in Patients With Metastatic Non-small Cell Lung Carcinoma

Metastatic non-small cell lung cancer (NSCLC) remains a highly heterogeneous disease with variable responses to immune checkpoint inhibitors, despite their transformative impact on patient outcomes since 2015. Radiotherapy has emerged as a potential synergistic partner for immunotherapy, based not only on its established local cytotoxic effects but also on its capacity to modulate the tumor microenvironment and activate systemic anti-tumor immunity.

Several preclinical and early clinical studies have illustrated how radiation may increase tumor antigen release, upregulate MHC (Major Histocompatibility Complex) class I molecules, and enhance T-cell priming. The abscopal effect, while rare, underscores the possibility that localized radiotherapy can induce immune-mediated tumor regression at distant, non-irradiated sites. These observations support a growing rationale for combining immune checkpoint inhibitors with radiotherapy in a therapeutic strategy that goes beyond additive effects, aiming instead for immune potentiation.

This retrospective, multicenter, observational study investigates whether real-world integration of radiotherapy into immunotherapy regimens improves survival outcomes in patients with metastatic NSCLC. The study is designed to reflect routine clinical practices across participating institutions, with radiotherapy administration (either concomitant or sequential) guided by multidisciplinary clinical decision-making rather than protocolized intervention. This pragmatic approach allows for exploration of a wide range of clinical scenarios and patient profiles, including variation in timing, dose, target site, and sequence of the radiotherapy-immunotherapy combination.

In addition to comparing overall survival (OS) and progression-free survival (PFS) between patients treated with immunotherapy alone versus those receiving additional radiotherapy, the study also seeks to characterize patterns of treatment response, including tumor control in non-irradiated sites, and to identify subgroups most likely to benefit from the combination strategy. Particular interest lies in the immune effect beyond the radiation field, which could serve as an indirect marker of enhanced systemic immune activation.

This study not only aims to generate meaningful insights into real-world treatment patterns and outcomes but also to provide a foundation for future prospective clinical trials. By better understanding how radiotherapy might modulate the immunotherapeutic response in metastatic NSCLC, we hope to refine patient selection, optimize treatment timing, and ultimately improve the effectiveness of immunotherapy in this challenging clinical setting.

Data will be extracted retrospectively from medical records and institutional databases. Collected data will include:

• Demographics: age, sex, smoking history
• Clinical data: performance status, TNM stage (classification system for classifying malignancy), histology, PD-L1 (Programmed Cell Death Ligang 1) status
• Immunotherapy details: agent, start date, treatment duration
• Radiotherapy details: date, site, dose, technique, concurrent/sequential timing
• Survival endpoints: OS (from start of immunotherapy to death), PFS (from start of immunotherapy to radiologic progression or death)
• Adverse events graded by CTCAE (Commun Terminology Criteria for Adverse Events) criteria
• Imaging reports and tumor response: RECIST v1.1 (Response Evaluation Criteria In Solid Tumor) or iRECIST

Statistical Analyses:

• Descriptive statistics: means, medians, frequencies
• Kaplan-Meier analysis for OS and PFS
• Cox proportional hazards regression for hazard ratio estimates
• Subgroup analyses by timing of radiotherapy, PD-L1 level, and other covariates
• Multivariate analysis adjusting for confounders A propensity score matching technique will be used to minimize selection bias by balancing key baseline characteristics between treatment groups. This will allow a more accurate estimation of the effect of radiotherapy, independent of potential confounders such as PD-L1 expression, histologic subtype, and performance status. Outcomes will be assessed in accordance with standardized criteria, and all imaging will be reviewed in multidisciplinary tumor boards to ensure consistency.

Ethical considerations:

This is a non-interventional study using retrospective, anonymized data. No additional procedures or patient contact are required. Institutional approvals and data protection regulations will be respected at all participating centers. The study complies with the General Data Protection Regulation (GDPR) and French data privacy laws.